1. Field of the Invention
The present invention relates generally to a remote plasma source for exciting a process gas into a plasma state. More particularly, the present invention relates to a plasma applicator for delivering excited gas species into a processing chamber in which a substrate is to be processed.
2. Description of the Related Art
Plasma processing is an important tool of the semiconductor manufacturing industry. This processing uses electromagnetic radiation to strike a plasma that produces a reactive species that is used for such process steps as wafer etching. A plasma may be produced directly above the surface of the wafer within the process environment, or the plasma may be remotely generated in an applicator, and then conducted to the surface of the wafer.
FIG. 1 illustrates a known, remote plasma source 10 which can be used as a stand alone plasma source for cleaning, etching or depositing materials in a processing chamber 4 or in conjunction with other plasma sources inside or outside a processing chamber. The remote plasma source 10 generally comprises a microwave generator 2 coupled by a waveguide 11 in communication with a generally cylindrically-shaped resonant cavity or chamber 12.
The resonant chamber 12, generally defined by a microwave reflective shell such as an outer metal housing or cover 13, includes a microwave transparent tube 14 that extends down through the chamber 12 along its radial axis for the passage of gases to be activated or excited and delivered to the processing chamber 4. The tube 14 is typically made of a microwave transparent, dielectric material, such as sapphire, quartz, ceramic, borosilicate glass or the like. A compressible material layer 25 may be disposed between the outer shell 13 and the tube 14 to secure the two members while allowing for differences in expansion under a wide range of temperatures.
The housing 13 of the plasma source 10 has a removable first lid 20 with a gas inlet port 21 and a removable second lid 22 with a gas outlet port 23. The gas inlet and outlet ports 21 and 23 are typically aligned with and centered on the radial axis of the chamber 12. The gas inlet port 21 in the first lid 20 supplies low pressure precursor gases into the microwave transparent tube 14 in the resonant chamber 12 where the gases can be ionized. The gas outlet port 23 in the second lid 22 allows the excited gases to flow from the resonant chamber 12 into the processing chamber (not shown).
A rectangular, transverse slot 24 is disposed through a cylindrical central portion 6 of the outer metal cover 13 to inject microwave energy from the microwave generator through the internal microwave tube wall 14 to the cavity. The microwave energy enters the resonant chamber 12 through the cylindrical side wall of portion 6 to excite a gas provided therein into a plasma state.
A plurality of coolant passages 15 are disposed in the cylindrical walls of the central portion 6 of the outer metal cover 13 so that a cooling fluid may be passed through them in order to dissipate heat generated in the plasma cavity. The cooling fluid enters a coolant inlet port 16 whereupon it flows through an inlet manifold 17 disposed in the first lid 20, down parallel flow paths through the passages 15 to an outlet manifold 18 and exits via the coolant outlet port 19 disposed in the second lid 22.
FIGS. 2-6 depict another, known plasma applicator of a different design. Referring first to FIGS. 2 and 3, the plasma applicator 30 includes a removable, front cover plate 32, a removable, rear cover plate 33 and a central body member 31 having a resonant chamber 46. The central body member 31 and resonant chamber 46 are cylindrical in shape, the radial axis of which extends through the front and rear cover plates 32 and 33. A gas inlet port 34 and a gas outlet port (not shown) are formed on generally opposite sides of the cylindrical side walls of the body 31 and are typically centered approximately midway between the front cover plate 32 and rear cover plate 33. A coolant inlet port 35 and coolant outlet port 36 are located generally adjacent to one another on the same side of the body 31.
Situated between the front cover plate 32 and the body 31 are a microwave transparent window member 37 and an aperture plate 38 having a rectangular aperture 39 which is centered in the middle of the plate 38. The window member 37 is usually made of aluminum nitride, a material which is transparent to microwaves, yet substantially impermeable to the plasma gases typically contained within the resonant chamber 46. Three O-rings 40, 41 and 42, form a pressure-tight seal between the front cover plate 32, the window member 37, the aperture plate 38, and the body 31. As best seen in FIG. 6, the O-ring 40 is an aluminum member disposed in the front cover plate 32 and having teats 58 formed along opposing sides of the O-ring. A force is applied by the O-ring 40 against the window 37 which pushes it towards the O-ring 41 and the aperture plate 38.
The front cover plate 32 includes a plurality of cover plate bolt holes 43 for securing the cover plate 32 to the remainder of the assembly. A plurality of waveguide bolt holes 44 are also disposed in the front cover plate 32 in order to permit the attachment of the waveguide portion of a microwave generator (not shown) to the cover plate 32. Finally, a generally rectangular opening 45 is also disposed in the cover plate 32 in order to permit passage of microwaves from a microwave generator through the cover plate 32, the aluminum nitride window 37, the rectangular aperture 39 of the aperture plate 38 and into the resonant chamber 46.
FIG. 4 shows the end of the plasma applicator 30 containing the rear cover plate 33 assembly. Situated between the rear cover plate 33 and the body 31 are an aluminum nitride window 47 and a center plate 48 having a sensor port 49 disposed in the center of the plate 48. O-rings 50 and 51 are placed between the body 31, the center plate 48 and the aluminum nitride window 47 in order to form a pressure-tight seal. A microwave detector 52 is attached to the center of the rear cover plate 33 directly over a rear cover plate port 53 in order to receive and detect microwaves passing from the resonant chamber 46, through the sensor port 49, the aluminum nitride window 47 and the rear cover plate port 53. The detector 52 measures the amount of microwave energy in the chamber 46 thereby permitting the operator to make energy adjustments as operational conditions require.
FIG. 5 shows the coolant flow path of the plasma applicator 30. Coolant fluid, such as water, enters the body 31 via the coolant inlet port 35. The coolant then flows into a circular inlet manifold 55 which is formed within and encircles the body 31. From the inlet manifold 55 the coolant flows in parallel paths through a plurality of straight, parallel channels 56 to a circular outlet manifold 57 which, like the inlet manifold 55, encircles the body 31. The coolant exits through the coolant outlet port 36. This arrangement has some problems however. It has been noted by the present applicants that the water pressure in some channels can be greater than in others. It is believed that this can result in uneven water flow rates and uneven heat removal rates which in turn can cause localized hot spots within the body 31.
The use of aluminum nitride material for the window 37 presents certain other problems. While effective for its transparency to microwaves and impermeability to gases, aluminum nitride is a material which is typically relatively brittle and can crack or fracture relatively easily in the high temperature, operational environment of a microwave applicator.
A remote microwave plasma applicator of an improved design is provided. In one embodiment, the plasma applicator comprises a body having a cavity in which a plasma is generated from a gas. The body defines a coolant inlet port, a coolant outlet port and a coolant channel adapted to provide a series coolant flow path from the coolant inlet port to the coolant outlet port.
In one embodiment, the body is generally cylindrical in shape and the coolant channel provides a first flow path in fluid communication with a second flow path. The first flow path follows a generally circular path in a clockwise direction substantially around the circumference of the cylindrical body. The second flow path follows a generally circular path in a counter-clockwise direction substantially around the circumference of the cylindrical body.
In an alternative embodiment, the body has a proximate end opening adapted to admit microwave energy into the cavity and a distal end disposed generally on the opposite side of the cavity from the proximate end opening. The body defines a gas outlet port adapted to permit the flow of an excited gas out of the cavity and a gas inlet port adapted to admit a precursor gas into the cavity. The gas inlet port has a center axis disposed between the proximate end opening of the body and the midpoint between the proximate end opening and the distal end of the body.
In yet another embodiment, a window member is disposed at the proximate end opening and is substantially transparent to microwave energy. An aperture member is adjacent to the window member. The aperture member is adapted to transfer heat from the window member to the body and has an aperture with a generally circular or oval shape.
In still another embodiment, the window member has a substantially planar shape with a first side which faces the cavity, a second side and a perimeter edge. At least two pins are disposed between the perimeter edge of the window member and the body.
In yet another embodiment, an outer member is disposed adjacent to the second side of the window member. A ring member is compressed between the second side of the window member and the outer member. A seal member is disposed between the ring member and the second side of the window member and is adapted to prevent direct contact between the ring member and the window member.
In still another embodiment, a first flange is disposed on the body and a second flange is disposed on the outer member. A clamp is adapted to removably attach the second flange to the first flange.
In yet a further embodiment, the body is integrally formed as a single piece of metal.